Conventional refrigeration systems have a compressor which pumps refrigerant vapour to condense to liquid refrigerant. The liquid refrigerant flows through the liquid line into a receiver tank where sufficient liquid refrigerant is stored to maintain a liquid seal for the liquid line through which the liquid refrigerant flows to a thermostatic expansion (TX) valve which controls the flow of liquid refrigerant to an evaporator coil, where pressure is reduced to cause the liquid refrigerant to vaporize with consequent absorption of heat. The refrigerant vapour flows through a suction line to the compressor. This is a dynamic closed loop, with a change in state of the refrigerant from vapour to liquid emitting heat, then from liquid to vapour absorbing heat.
When the liquid refrigerant passes through the TX valve and vaporizes with consequent heat absorption in the evaporator coil, the temperature of the liquid refrigerant has first to be lowered to the vaporizing temperature, thereby causing a loss in the cooling efficiency of the refrigeration system. The higher the liquid refrigerant temperature the greater the loss of efficiency. To assist in minimizing this problem, it is well known to use a liquid line to suction line heat exchanger in which the temperature of the liquid in the liquid line is lowered by the gas at lower temperature in the suction line.
In refrigerated merchandising cases in supermarkets, it is conventional to use heat exchangers which cool the liquid refrigerant by close thermal contact with the colder refrigerant suction gas. In such merchandising cases, the reduction of liquid refrigerant temperature has been believed to increase the efficiency of the refrigeration system by at least about 8%, thereby producing worthwhile savings in operating costs.
As part of a general investigation into possible ways of still further increasing efficiency of refrigeration systems in refrigerated merchandising cases in supermarkets, the applicant investigated the temperature difference between the temperature of the liquid refrigerant in the liquid line entering the heat exchanger and the temperature of the liquid refrigerant in the liquid line leaving the heat exchanger in a typical supermarket installation. It was expected that this would be a significant temperature difference, with the magnitude of the temperature difference indicating the increase in efficiency obtained by use of the heat exchanger. Applicant was surprised to find that, contrary to expectations, there was no meaningful temperature difference, with there consequently being virtually no benefit obtained by use of the heat exchanger. This finding is probably true for tens of thousands of heat exchangers currently in use in refrigerated display cases in supermarkets.